ceremonies in new york, virginia, and pennsylvania pay tribute to the 2,752 victims killed when terrorists hijacked four commercial planes that attacked the u.s. in lower manhattan 9/11 families gather at a park adjacent to ground zero. throughout the morning in shanksville, pennsylvania where united 93 flight crashed, michelle obama and laura bush will honor a ceremony to honor the passengers that fought back. plans to rebuild at ground zero are moving forward. the centerpiece, one world trade center, is expected to be completed by 2013, but with each construction step forward, there remains a connection to the past. steel beams pulled from the rubble were permanently installed this week at the entrance of the national september 11th memorial and museum slated to be finished in 2012. >> it is going to be a memorial that we will all be proud of and a memorial that will inspire people around the world. >> and always remind them never to forget. president obama also signed a probleming clamation making september 10th through 12th national days of prayer and remembrance, calling on americans